[Buildroot] [PATCH 2/3] fs/squashfs: align size to 1MiB

[Yann E. MORIN]

Arnout, All,

On 2017-07-11 23:31 +0200, Arnout Vandecappelle spake thusly:
> On 11-07-17 22:42, Yann E. MORIN wrote:
> [snip]
> > $ qemu-system-arm -M vexpress-a9 -smp 1 -m 256 -kernel output/images/zImage -dtb output/images/vexpress-v2p-ca9.dtb 
> > -drive file=output/images/rootfs.squashfs,if=sd,format=raw
> > -append "console=ttyAMA0,115200 root=/dev/mmcblk0" -serial stdio -net
> nic,model=lan9118 -net user
> [snip]
> > mmcblk0: mmc0:4567 QEMU! 2.25 MiB
> 
>  Hm, you're emulating an SD card here. I'm not sure how qemu deals with emulated
> devices where the backing file doesn't have a size that corresponds to what the
> kernel driver expects... Possibly the last bit is just chopped off, which might
> lead to an issue like this...
> 
>  Does it also happen when you emulate it as an IDE device? Or even better, does
> it also happen on actual hardware?
> 
>  I don't feel good doing such padding just to make qemu happy when actual
> hardware doesn't need it...

So, I booted a rpi2 with a squashfs as rootfs, and it boots all the way
to a login prompt, and the image is not padded to 256KiB:

    $ ls -l images/rootfs.squashfs
    -rw-r--r-- 1 ymorin ymorin 20086784 juil. 11 23:42 images/rootfs.squashfs

Which means that this is a qemu limitation...

I've marked this patch and the next one as rejected.

Thanks! :-)

Thomas, so what do you want to do in the runtime testing infra: I would
be wary to add a call to truncate in all cases that generate a squashfs
image (I already have 6 of them).

Would it be acceptable that the emulator class first truncates its input
image to pad it to a 1MiB boundary, whatever the input image?

Regards,
Yann E. MORIN.

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